1. Field of the Invention
The present invention relates to a flexible printed circuit composed of a flexible insulating film and a circuit formed thereon and a method of manufacturing the same, and particularly to a flexible printed circuit with an improved reliability obtained from prevention of separation of a sheet material attached on the flexible printed circuit and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, printed circuit boards and methods of manufacturing the same have been known for improving the reliability of flexible printed circuits (FPC) (e.g., see JP2005-268416A (pp. 3-6, FIGS. 1-3)). A printed circuit board is composed of a circuit board on which a circuit pattern is formed, and a coverlay film having an opening and attached on a surface of the circuit board.
A projection is formed on the surface of a portion of the circuit pattern to which the opening is aligned, and an adhesive agent of the coverlay film is prevented by the projection from flowing into the opening. Also known are a releasing film and a method for manufacturing a circuit board (e.g., see JP2007-98816A (pp. 4-12, FIGS. 1-3)).
The releasing film is used when a circuit board is manufactured using a core base board having a convex circuit of an average height of A μm, and comprises a first layer to a third layer layered in this order. This film is designed such that when the first layer and the circuit are contact-pressed at a pressure of 4 MPa and a temperature lower than a melting point of a polyester resin by 50° C., A/B×100 is equal to 70% or greater, where B is an average height in μm at which the first layer is intruded into the gap of the adjacent convex circuit. According to this document, this can prevent leakage of the adhesive agent, etc.
Meanwhile, flexible printed circuits still suffer from a problem that a sheet material 200 attached on a board body 100 comes off therefrom, as shown in FIG. 9. The cause of this problem is considered to be as follows. That is, an adhesive agent 300 located between a board surface 100a of the board body 100 and an adhesive surface 200a of the sheet material 200 leaks from the side of an end surface 200b of the sheet material 200 onto the board surface 100a in a tapered shape.
Then, when a stress or the like is applied to an edge 200c of the end surface 200b of the sheet material 200 that is closer to the board body 100, a crack 301 forms in the leaked adhesive agent 300. The adhesive agent 300 breaks from this crack 301 and the sheet material 200 gets peeled from the board body 100.
Accordingly, there is a demand for a measure against leakage of an adhesive agent caused in the printed circuit board disclosed in JP2005-268416A and in the releasing film disclosed in JP2007-98816A, and for a measure for more effectively preventing separation of a sheet material from a flexible printed circuit to improve reliability.
To solve the problem of the conventional techniques described above, an object of the present invention is to provide a flexible printed circuit and a method of manufacturing the same which can improve reliability by preventing separation of a sheet material attached on a flexible printed circuit.